Modeling and simulations of new electrostatically driven, bimorph actuator for high beam steering micromirror deflection angles

Abstract

There are numerous applications for micromirror arrays seen in our everyday lives. From flat screen televisions and computer monitors, found in nearly every home and office, to advanced military weapon systems and space vehicles, each application bringing with it a unique set of requirements. The microelectromechanical systems (MEMS) industry has researched many ways micromirror actuation can be accomplished and the different constraints on performance each design brings with it. This paper investigates a new "zipper" approach to electrostatically driven micromirrors with the intent of improving duel plane beam steering by coupling large deflection angles, over 30°, and a fast switching speed. To accomplish this, an extreme initial deflection is needed which can be reached using high stress bimorph beams. Currently this requires long beams and high voltage for the electrostatic pull in or slower electrothermal switching. The idea for this "zipper" approach is to stack multiple beams of a much shorter length and allow for the deflection of each beam to be added together in order to reach the required initial deflection height. This design requires much less pull-in voltage because the pull-in of one short beam will in turn reduce the height of the all subsequent beams, making it much easier to actuate. Using modeling and simulation software to characterize operations characteristics, different bimorph cantilever beam configurations are explored in order to optimize the design. These simulations show that this new "zipper" approach increases initial deflection as additional beams are added to the assembly without increasing the actuation voltage.

Post Fabrication Processing of Foundry MEMS Structures Exhibiting Large, Out-of-Plane Deflections

“…The post-processing steps outlined above were repeated for an electrostatically actuated design utilizing a beam structure in the form of a folded cantilever beam or serpentine layout [4]. The baseline electrostatic design fabricated in the PolyMUMPs fabrication process resulted in an out-of-plane deflection of ~140 µm as shown in the Comsol image in Figure 5a,b illustrates a 5 × 4 array of these structures with a close up view shown on the right of a single actuation assembly.…”

Segmented Control of Electrostatically Actuated Bimorph Beams

“…The device is actuated by creating a potential difference resulting in an electrostatic force between the zipper beams and the underlying electrode causing the beams to deflect down. As shown in Figure 1, the zipper approach allows a large vertical displacement of up to 175 μm to be achieved within a relatively small area [1]. The current design lacks the ability to control and measure the amount of beam deflection.…”